1. Field of the Invention
The present invention relates to a sealed battery manufacturing method performing an introduction step of introducing a detection gas into a battery container from an opening that is opened outwardly.
2. Description of Related Art
Conventionally, in a manufacturing process of a sealed battery, sealing performance of a battery container is inspected for purposes of preventing deterioration of battery performance due to moisture intrusion into the battery container. At this time, in the manufacturing process of the sealed battery, a detection gas (e.g., helium or the like) is introduced into the battery container in advance, so as to check whether or not the detection gas leaks from the battery container. A technique to introduce a detection gas is described in Japanese Patent Application Publication No. 2002-117901 (JP 2002-117901 A), for example.
JP 2002-117901 A describes such a technique that an injection nozzle is attached to an electrolyte injection port, and then electrolyte is injected into a battery can (a battery container) from the injection nozzle and helium is introduced into the battery can. Further, JP 2002-117901 A describes that the injection nozzle is removed from the electrolyte injection port, and the electrolyte injection port is sealed by laser welding means.
JP 2002-117901 A describes a configuration in which helium is introduced from the injection nozzle attached to the electrolyte injection port, that is, a configuration in which helium is introduced from an upper part (outside the battery can) of the electrolyte injection port. Accordingly, before the electrolyte injection port is sealed, much helium, which is lighter than air, leaks from the electrolyte injection port.
As a method for reducing a leakage of helium, the following method is considered. That is, as illustrated in FIG. 14, a nozzle configured to be able to inject helium is inserted into an electrolyte injection port and a magnetic valve for opening and closing a helium supply passage is opened so as to inject helium from the nozzle at a predetermined pressure for a given time. In this case, the predetermined pressure is set to a large pressure to some extent, so that the helium is injected from the nozzle vigorously to such an extent that the helium reaches a position away from the electrolyte injection port.
A pressure inside the battery can is increased due to the helium injection. In view of this, just after the helium injection is started, the pressure inside the battery can is small. In this case, when the helium is injected at the predetermined pressure, the helium at the predetermined pressure is supplied at once right after the helium injection is started, as illustrated in FIG. 14. This causes a flow speed of the helium injected from the supply nozzle becomes fast suddenly, and after that, the flow speed is maintained stably at a constant speed.
In this case, the flow speed of the helium becomes too fast right after the helium is injected and a flow speed of airflow caused in the battery can due to the helium injection and going outside via the electrolyte injection port becomes fast (see an arrow shown inside the electrolyte injection port in FIG. 14). As illustrated in FIG. 15A, the fast airflow may catch the electrolyte attached to an inner side surface of the battery can along the injection nozzle at the time of the injection, and blow off the electrolyte outside the battery can. Accordingly, in this case, when the helium is introduced, the electrolyte may be attached to a peripheral part of the electrolyte injection port on an outer side surface of the battery can (see electrolyte shown in FIG. 15B).
In this case, when the electrolyte injection port is sealed by the laser welding means, its heat is also given to the electrolyte thus attached to the outer side surface of the battery can. The electrolyte attached to the outer side surface of the battery can is vaporized by the heat in a melting portion and expands rapidly to go outside from the melting portion. This causes a molten material (e.g., aluminum or the like) of the battery can to bump.
That is, in this case, poor welding may occur at the time of sealing the electrolyte injection port.